"I'm preparing myself for the school shooting," he wrote, according to the newspaper. "I can't wait. My aim has gotten much more accurate ... I can't wait to walk into that class and blow all those (expletives) away."

His grandmother showed officers parts of the journal where O'Connor allegedly drew up plans to shoot students and use homemade explosives at the school.

"I need to make this count," O'Connor wrote, according to the paper. "I've been reviewing many mass shootings/bombings (and attempted bombings) I'm learning from past shooters/bombers mistakes."

Remembering the victims of the Florida high school massacre

In addition to the journal, investigators found a rifle inside a guitar case as well as grenades.

Public defender Rachel Forde said the weapon and the grenade shells were legally owned, according to the Daily Herald. The "musings and ventings" in the journal do not support an attempted murder charge, she added, according to the newspaper.

Authorities believe that O'Connor committed an armed robbery to fund his plan, according to the newspaper. When he was arrested, a knife and marijuana were found on his person.

Cops say that O'Connor was planning to die during his attack on the school. His bail was set at $5 million.

He was arrested at ACES High School in Everett, Washington. (KING 5)

His arrest came one day before 17 people were killed in a school shooting in Florida, the 18th school shooting so far this year.

"Our main thing right now is gratitude, especially to the grandmother," Mukilteo School District spokesperson Andy Muntz told the Daily Herald. "That couldn't have been easy for her to do. The Everett police also did a wonderful job. That combination may have saved a lot of lives."